That is the question roiling the world of organic farming, and the answer could redefine what it means to farm organically.

At issue is whether produce that relies solely on irrigation to deliver nutrients to plants — through what is known as hydroponic and aquaponic systems — can be certified organic. The National Organic Standards Board, an advisory group that makes recommendations to the secretary of agriculture, discussed it at its meeting in St. Louis last week.

On one side are the growing number of big and small growers raising fruits and vegetables in these soil-free systems. They say their production methods are no different from those of farmers who grow plants in dirt — and, they add, they make organic farming more sustainable by, for instance, reducing water use.

“Soil to me as a farmer means a nutrient-rich medium that contains biological processes, and that doesn’t have to be dirt,” said Marianne Cufone, the executive director of the Recirculating Farms Coalition, which lobbies for aquaculture.

Not so, say the farmers who have spent years tending their soil. They argue that organic production is first and foremost about caring for the soil, which produces environmental benefits that go beyond growing plants.

“Soil has always been the basis of organic production,” said Steve Sprinkel, an organic farmer in Ojai, Calif. “The soil is alive and releasing micronutrients to plants that use their roots to scavenge and forage those things, and so taking care of the soil is the bedrock of organic farming.”

U.S. sales of organic food hit $40 billion last year, sending grocers scrambling to find enough organic produce to fill their cases. Keeping up with the demand is difficult and expensive. Financiers and entrepreneurs, many of them from Silicon Valley, have started pouring money into these alternative systems.

Whether the soil-free systems help bring down the price of organic products remains to be seen. Equipment like lighting and organic nutrients are expensive — soil growers count on their dirt to deliver some of those nutrients at no cost — and hydroponically and aquaponically grown fruits and vegetables usually are sold for the same price as organic produce grown in dirt.

The decision about whether these growing systems can continue to be certified falls to the U.S. Department of Agriculture, which has a task force to study the issue.